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Old 10-15-2013, 08:33 PM
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1975_jeep_j10 1975_jeep_j10 is offline
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Oil Pressure Problems

My 77 j20 with a 360 is having oil pressure issues. Truck was sitting for 1 or more years without running but it had oil in it and everything wasn't seized. It is a pretty worn out motor but it started right up when i got it home but it ran with a bad miss but that has been resolved. I changed the oil with 10w-30 and a wix filter. My gauge says about 60 psi of oil pressure cold and around 40 hot, but just the other day, the pressure went from 60 to exactly zero really slowly, and then about 5 min later at idle it rose slowly to 60 again and stayed there. My oil is full on the dipstick. The outside of the oil pump is not wet but its just covered in years of oily build up on it and I cant really find a really noticable leak that would create a huge problem. What could be the cause of this wierd loss of oil pressure?

PS: I have already changed my pressure sender because the old one got full of gunk when I put risilone through the motor before I did my oil change.
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Old 10-15-2013, 08:43 PM
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Might have had more gunk block the sender port or there is a problem elsewhere in the gauge system.
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Old 10-16-2013, 10:08 AM
JeepWrencher JeepWrencher is offline
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The oil pressure gauge on our FSJs is like seeing a light about 2 miles away. You know something is there but no idea what it really is.

When I started having inconsistent readings I checked with a manual gauge and found the FSJ one was at least 20psi off and got worse the lower the pressure was. So when I would sit at a hot idle it would actually not read anything on the gauge at all. Manual gague would read ~15psi at the same hot idle.

I replaced my sender checked grounds and power and no improvement. I have considered a replacement gauge itself, not sender, from BJ's but now I'm used to how the gauge will read when there are issues so I don't really care about the number.

Also, I have almost 250k miles on my 360 just did a oil pump rebuild a couple weeks ago, super easy and cheap. My recommendation would be mechanical gauge and pump rebuild.
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Old 10-16-2013, 12:52 PM
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Zero oil pressure will let the lifters collapse and make a heck of a racket. Unlikely you actually had zero OP without a lot of clatter.

I say it's a gauge issue. Check the connections, replace the sender, convert to a mechanical gauge.
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Old 10-17-2013, 05:25 PM
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Quote:
Originally Posted by 1975_jeep_j10
.... What could be the cause of this wierd loss of oil pressure?

PS: I have already changed my pressure sender because the old one got full of gunk when I put risilone through the motor before I did my oil change.

If you had full oil level, its unlikely you really lost and regained oil pressure as you described. The oil pump has only two modes of failure: 1) Slo-o-o-owly decreasing pressure from internal wear occurring over years and many miles, and 2) sudden death...you're done for good.

Since you replaced the sender, the next thing I'd look at is the reliability of the connector itself and/or its contact on the sender. Its a decades-old factory crimp-on. Years ago on a previous waggy I had unlikely pressure variations, so I cut the connector off, stripped back the wire a few inches and SOLDERED on a new female...and good to go. Fast forward to my current '88: I added a splitter block (or whatever you call it) and now have both original gauge and mechanical, which track pretty close.
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